1. Field of the Invention
The present invention relates to a poduct for topical application which can release a cosmetic and/or dermatological active agent on the skin, and to the use of the product for the cosmetic and/or dermatological treatment of the skin, including the scalp.
2. Discussion of the Background
It is well-known to introduce active agents into cosmetic and/or dermatological compositions in order to allow specific skin treatments, for example to combat the drying-out, ageing or pigmentation of the skin, to treat acne or certain skin diseases (eczema, psoriasis), to combat excess weight or to promote the restructuring of the skin or its cell renewal.
For example, ascorbic acid (or vitamin C) is known to stimulate the growth of connective tissue, and in particular that of collagen. It thus strengthens the skin tissue's defences against external attack such as ultraviolet radiation or pollution. It is also used to remove skin pigmentation and marks, as well as to promote cicatrization of the skin.
It is also known that the application of retinol, or vitamin A, in particular combats ageing of the skin and certain skin conditions such as acne or keratinization or cicatrization disorders.
In addition, tocopherols, such as vitamin E, are known to have antioxidant properties with respect to the phospholipids of the cell membrane and radical-scavenging properties (see "Radicaux libres et Vitamine E [Free Radicals and Vitamin E]" by J. B. Chazan and M. Szulc-Cah. Nutr. Diet. 1987, 6, 1, XXII, pages 66 to 76).
Unfortunately, certain active agents, and in particular those mentioned above, are unstable and are sensitive to external factors such as light and heat. This instability goes against the desired efficacy and, what is more, can be the source of unpleasant sensations for the user, for example when the instability of the active agent leads to changes in the color and/or odor of the composition containing it.
Thus, various means have been envisaged to stabilize these active agents. One of these means consists, for example, in blocking the reactive site of the active agent by esterification with, in particular, phosphate, sulphate or alkyl derivatives and in using these derivatives in place of the free active agent. Unfortunately, these derivatives are less effective than the free active agent.
It has also been envisaged to use precursors of such active agents, which, after applying them to the skin, are cleaved by the skin enzymes and thus release the free active agent. Thus, EP-A-487,404 discloses the use of a glucosyl derivative of ascorbic acid in dermatological compositions, which is readily hydrolysed by the skin enzymes and thus capable of releasing ascorbic acid when these compositions are applied to the skin. However, the use of such derivatives does not allow a rapid release of ascorbic acid in sufficient quantity on the surface of the skin.
There is thus a need for a topical application product containing vitamins used in cosmetics and/or dermatology, in which these vitamins conserve all their properties and thus their efficacy over time.
EP 710,478 describes that the use of a specific enzyme, lipase, combined with esters of unstable vitamins, such as vitamin A (retinol) or vitamin C (ascorbic acid), avoids the drawbacks of previously known compositions.